stackoverlow 3 table join

select_photos_categories2.php

<?php
  require_once  'mysqli_connection.php';
  ini_set('display_errors', 1);
  ini_set('display_startup_errors', 1);
  error_reporting(E_ALL);
  
  //define table
    $tbl = "photos";
    $joinsTbl = "joins";
    $catsTbl = "categories";

    //write query
$query = "SELECT $tbl.photoID, $tbl.photoSRC, $tbl.photoCredit, $joinsTbl.categoryID,  
          GROUP_CONCAT($catsTbl.photo_category SEPARATOR ',') AS categories
          FROM $tbl
          LEFT JOIN $joinsTbl
          INNER JOIN $catsTbl
             ON $joinsTbl.categoryID = $catsTbl.categoryID
             ON $tbl.photoID = $joinsTbl.photoID
          GROUP BY $tbl.photoID
          LIMIT 100";
  //prepare statement, execute, store_result
    if($displayStmt = $mysqli->prepare($query)){
      $displayStmt->execute();
      $displayStmt->store_result();
      $numrows = $displayStmt-> num_rows;
      //echo("<br>results: $numrows");
      //echo($displayStmt->error);
    }      
    
    $photosArray = [];
  //bind results
    $displayStmt->bind_result($photoID, $photoSRC, $photoCredit,  $categoryID, $categories);
  
    //fetch results
    while($displayStmt->fetch()){
      $photosArray[] = ['photoID'=>$photoID, 'photoSRC'=>$photoSRC, 'photoCredit'=>$photoCredit, 'categoryID'=>$categoryID, 'categories'=>$categories, ];
    }

    echo(json_encode($photosArray));

  ?>